Conductor composition, a mounting substrate and a mounting structure utilizing the composition

ABSTRACT

A conductor composition being able to easily secure the conductivity at the same level as an Ag bulk at low temperature process, a mounting substrate utilizing the conductor composition and a mounting structure utilizing the conductor composition are provided. In a mounting structure, wherein one or more electrodes ( 11 ) of a mounting substrate ( 10 ) and one or more surface mounting components ( 20 ) are connected through a conductor composition ( 30 ), and one or more surface wirings ( 14 ) of the mounting substrate ( 10 ), one or more inner-layer wirings ( 13 ) and one or more via conductors ( 12 ) are formed with the conductor composition, the conductor composition contains conductive particles with electrical conductivity, and the conductive particles are composed of low crystallized Ag fillers with the crystal size of 10 nm or less.

TECHNICAL FIELD

The present invention relates to a conductor composition containingconductive particles with electrical conductivity, a mounting substratewherein wiring parts are formed by utilizing such a conductorcomposition, and a mounting structure wherein a component is mounted byutilizing such a conductor composition.

BACKGROUND

In general, this kind of a conductor composition comprises conductiveparticles with electrical conductivity and a solvent. Specificallyspeaking, for example, an electroconductive adhesive is known, whereinAg fillers with particle diameters at the level of a micron or asub-micron (in the order of 1 μm to 10 μm) was dispersed in a solventand a binder resin such as an epoxy resin, etc. (refer to e.g. Japaneseunexamined patent publication No. 2000-319622).

Further, as this kind of the conductor composition, a paste compositionhas been suggested, wherein fine metal particles with a mean particlediameter from 1 nm to 100 nm were covered on the surface with an organiccompound which was able to coordinate with a metal atom contained infine metal particles, and were stably dispersed in a liquid (refer toe.g. Japanese unexamined patent publication No. 2002-299833).

Such an electroconductive adhesive was used in order to form anelectrical connect between a surface mounting component and the mountingsubstrate, by being placed between them, and to construct the mountingstructure, when the surface mounting component was mounted on anelectrode formed on one side of the mounting substrate.

This kind of conductor composition has been used also to form surfacewiring, inner-layer wiring and a via conductor on a mounting substratesuch as a print substrate, a ceramic substrate etc.

In the above-mentioned general conductor composition such as e.g. theelectroconductive adhesive containing the Ag fillers, a connection wascompleted by being placed on the substrate, with steps of heating afterbeing applied on a substrate such as an electrode, etc., evaporating asolvent and curing a binder resin.

Herein, a curing treatment for the electroconductive adhesive was, ingeneral, carried out under a low temperature (e.g. about 150° C.)necessary to remove the solvent, or cure the binder resin.

In a case where such a process under the low temperature was achieved,an electrically conducting structure at the treated electroconductiveadhesive was due to connections between Ag filler particles (conductiveparticles). Due to the connections, an electric resistance at theelectroconductive adhesive dominantly depended on the contact resistancebetween these Ag filler particles.

Therefore, the conductivity of the electroconductive adhesive wasapproximately two orders of magnitude lower than the inherentconductivity of Ag, i.e. the conductivity at the same level as in an Agbulk. Further, for the electrically conducting structure between theelectroconductive adhesive and the substrate, there has been a problemof low reliability of the connection, due to electrical conduction bycontact between the substrate and the Ag fillers.

For these problems, when the electroconductive adhesive (the conductorcomposition) is processed, it is deemed to be better to treat theadhesive at a temperature high enough to melt the conductive particlesof the Ag fillers. It seems that, by the process, the electricallyconducting structure at an inner part of the electroconductive adhesiveand between the electroconductive adhesive and the substrate becomes astructure for an electrical conduct between the Ag fillers mutuallymelted together, and conductivity at the same level as Ag bulk can beobtained in the electroconductive adhesive.

However, in order to achieve such a melting situation, it is necessaryto increase the temperature for treating the electroconductive adhesiveto, for example, close to the melting point of Ag (about 800° C.).Considering the heat resistances of an electronic component, which formsthe substrate material, and the substrate, such a process is notpractical.

Against that, as described in Japanese unexamined patent publication No.2002-299833, a conductor composition composed of only fillers(conductive particles) with a particle size of the order of nanometerhas been suggested. The composition substantially had a structurewherein only the fillers with a smaller size, of the order of nanometer,than conventional particles, with a particle size of the order ofmicron, were dispersed in a solvent and a binder resin.

Accordingly, it is expected to have fillers melted together by makingthe fillers small in the order of nanometer, and decreasing the meltingtemperature of the fillers themselves, even if they were treated at alow temperature (e.g. about 150° C.) like the low temperature forprocessing the conductor composition mentioned above.

However, in a case of the conductor composition composed of onlynanometer order fillers, their handling is difficult due to the smallsize of the filler particles, and their cost is higher in comparisonwith the conventional micron order filler particles.

As the filler particle size of the order of nanometer is much smallerthan the conventional filler particles, the small filler's dispersingproperty, into the solvent and the binder resin, is poor. As a result,it has been difficult to obtain a practical conductivity, owing to thefiller particles being unevenly distributed in the conductorcomposition, and the filler particles do not evenly melt together.

Therefore, considering the above-mentioned problems, the presentinvention was achieved to provide a conductor composition which caneasily secure conductivity at the same level as Ag bulk with a lowtemperature treatment, a mounting substrate utilizing such a conductorcomposition, and a mounting structure utilizing such a conductorcomposition.

SUMMARY OF INVENTIONS

In order to achieve the purpose mentioned above, in the inventionaccording to claim 1, for a conductor composition comprising conductiveparticles (30 a) with electrical conductivity and a solvent, theconductive particles (30 a) are composed of low crystallized Ag fillers(31) of which the crystal size is 10 nm or less.

Herein, the crystal size of each of the low crystallized Ag fillers (31)is the size of the crystal particle of one filler particle, and it isbased on a result of measurement by X-ray diffraction that the crystalsize is 10 nm or less.

In the past, in general, the crystal size of Ag fuller utilized in thiskind of the conductor composition was several tens of nanometers ormore, and Ag fillers (31) in the present invention comprise particleshaving a smaller size, in other words, being more crystallized than theconventional particles.

Based on studies by the inventors of the present invention, while adetailed mechanism has not been found, by utilizing the conductiveparticles (30 a) composed of the low crystallized Ag fillers (31) with aparticle size of 10 nm or less, high conductivity can be obtained byfusing or sintering Ag, with a treatment at a low temperature, at thesame level as the conventional conductor composition composed of onlyfillers with a particle size of the order of nanometer mentioned above,even if the particle size of the conductive particles (30 a) is in theorder of micron.

In other words, according to the invention, a conductor composition canbe provided which can easily ensure the conductivity at the same levelas an Ag bulk by a low temperature process.

In the invention described in claim 2, for the conductor compositionaccording to claim 1, conductive particles (30 a) comprise lowcrystallized Ag fillers (31) and fine Ag particles (33) with a particlesize of the order of nanometer adhering on surfaces of core particleswhich are crystallized Ag fillers (31).

As mentioned above, it can be achieved, as an effect, that the Agparticles (33) can be melted at a low temperature due to being made inthe order of nanometer, by locating the fine Ag particles (33) havingthe size of the order of nanometer around the low crystallized Agfillers (31) described in claim 1, and it is further possible to realizehigh conductivity by the low temperature process. In other words, in thepresent invention, it is preferable to process at a lower temperature.

In the invention described in claim 3, as the conductor compositionaccording to claim 1 or claim 2, each of the low crystallized Ag fillers(31) has the size of the particle diameter of 0.1 μm or more and 20 μmor less.

In the invention described in claim 4, at the conductor compositionaccording to any of claims 1-3, each of the low crystallized Ag fillers(31) is in the form of a sphere or a flake.

In the invention described in claim 5, at the conductor compositionaccording to any of claims 1-4, each of the fine Ag particles (33) has aparticle diameter in the range of 1 nm or more and 50 nm or less.

In the invention described in claim 6, as the conductor compositionaccording to any of claims 1-5, the amount of the adhered fine Agparticles (33) is 50 wt % or less of the low crystallized Ag fillers(31).

As described in the inventions according to claims 3-6, the size and theshape of the low crystallized Ag fillers (31), and the size and theamount of the fine Ag particles (33) can be concretely realized.

In the invention described in claim 7, the conductor compositionaccording to any of claims 1-6 features that the conductor compositioncontains a binder resin (32) with the conductive particles (30 a) andthe solvent, and is applied as an electroconductive adhesive.

In the invention described in claim 8, at a mounting structure utilizinga conductor composition comprising a mounting substrate (10) having oneor more electrodes (11) on one side of the substrate (10), and one ormore surface mounting components (20) mounted on the electrode(s) (11)of the mounting substrate (10), wherein the electrode(s) (11) and one ormore surface mounting components (20) are bonded through a conductorcomposition (30), the conductor composition comprises conductiveparticles (30 a), and the conductive particles (30 a) are composed of alow crystallized Ag fillers (31) of which the crystal size is 10 nm orless.

According to the present invention, as in the invention described inclaim 1 above, by utilizing the conductive particles (30 a) composed ofthe low crystallized Ag fillers (31) with a size of 10 nm or less, highconductivity can be obtained by fusing or sintering Ag, with a treatmentunder a low temperature in the same level as the conventional conductorcomposition composed of only filler particles with the size in the orderof nanometer mentioned above, even if the particle size of theconductive particles (30 a) is in the order of micron.

In other words, according to the present invention, a conductorcomposition can be provided, which can easily ensure the resistance atthe same level as Ag bulk by a low temperature process.

In the invention described in claim 9, for the mounting structureutilizing the conductor composition according to claim 8, the conductiveparticles (30 a) comprise the low crystallized Ag fillers (31) and thefine Ag particles (33) with a particle size of the order of nanometeradhering on surfaces of core particles which are the crystallized Agfillers (31).

According to the invention, based on the same reason as of the inventiondescribed in claim 2, the mounting structure is provided, which utilizesthe preferable conductor composition that can be treated at lowertemperature.

In the invention described in claim 10, in the mounting structureutilizing the conductor composition according to claim 8 or claim 9,each of the low crystallized Ag fillers (31) has the size of theparticle diameter of 0.1 μm or more and 20 μm or less.

In the invention described in claim 11, in the mounting structureutilizing the conductor composition according to any of claims 8-10,each of the low crystallized Ag fillers (31) is in the form of a sphereor a flake.

In the invention described in claim 12, for the mounting structureutilizing the conductor composition according to any of claims 8-11,each of the fine Ag particles (33) has the particle diameter in therange of 1 nm or more and 50 nm or less.

In the invention described in claim 13, for the mounting structureutilizing the conductor composition according to any of claims 8-12, theamount of the adhered fine Ag particles (33) is 50 wt % or less of thelow crystallized Ag fillers (31).

In the invention described in claim 14, for the mounting structureutilizing the conductor composition according to any of claims 8-13, theconductor composition comprises a binder resin (32) with the conductiveparticles (30 a) and the solvent, and is applied as an electroconductiveadhesive.

Further, in the invention described in claim 15, for a mountingsubstrate utilizing a conductor composition wherein one or more surfacewirings (14) and one or more inner-layer wirings (13) and one or morevia conductors (12) are formed, the conductor composition containsconductive particles (30 a) with electrical conductivity, and theconductive particles (30 a) are composed of low crystallized Ag fillers(31) of which the crystal size is 10 nm or less.

According to the present invention, just as the invention described inclaim 1 above, by utilizing the conductive particles (30 a) composed ofthe low crystallized Ag fillers (31) with a particle size of 10 nm orless, high conductivity can be obtained by fusing or sintering Ag, witha treatment under a low temperature at the same level as theconventional conductor composition composed of only filler particleswith the size in the order of nanometer mentioned above, even if theparticle size of the conductive particles (30 a) is in the order ofmicron.

In other words, according to the present invention, a conductorcomposition can be provided which can easily ensure the resistance atthe same level as an Ag bulk by the low temperature process.

In the invention described in claim 16, for the mounting substrateutilizing the conductor composition according to claim 15, theconductive particles (30 a) comprise the low crystallized Ag fillers(31) and fine Ag particles (33) with a particle size of the order ofnanometer adhering on surface of core particles which are thecrystallized Ag fillers (31).

According to the invention, based on the same reasons as of theinvention described in claim 2, a mounting substrate is provided whichutilizes the preferable conductor composition that can be treated atlower temperature.

In the invention described in claim 17, for the mounting substrateutilizing the conductor composition according to claim 15 or claim 16,each of the low crystallized Ag fillers (31) has the size of theparticle diameter of 0.1 μm or more and 20 μm or less.

In the invention described in claim 18, for the mounting substrateutilizing the conductor composition according to any of claims 15-17,each of the low crystallized Ag fillers (31) is in the form of a sphereor a flake.

In the invention described in claim 19, for the mounting substrateutilizing the conductor composition according to any of claims 15-18,each of the fine Ag particles (33) has the particle diameter in therange of 1 nm or more and 50 nm or less.

In the invention described in claim 20, for the mounting substrateutilizing the conductor composition according to any of claims 15-19,the amount of the adhered fine Ag particles (33) is 50 wt % or less ofthe low crystallized Ag fillers (31).

In the invention described in claim 21, for the mounting substrateutilizing the conductor composition according to any of claims 15-20,the conductor composition comprises a binder resin (32) in conjunctionwith the conductive particles (30 a) and the solvent, and is applied asan electroconductive adhesive.

A number in parenthesis for each of the means described above indicatesone example showing a correspondence with a concrete means inembodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional drawing to roughly illustrate a main part of amounting structure utilizing a conductor composition according to thefirst embodiment of the present invention.

FIG. 2 shows a schematic drawing to illustrate an electro-conductiveadhesive (conductor composition) before curing.

FIG. 3 shows a process chart to show a method for assembling a mountingstructure shown in FIG. 1.

FIG. 4 shows a sectional drawing to roughly illustrate the mountingstructure utilizing a conductor composition according to the secondembodiment of the present invention.

FIG. 5 shows a process chart to show a method for manufacturing amounting substrate in a mounting structure shown in FIG. 4.

DETAILED DESCRIPTION

Further, embodiments of the present invention are explained, by usingdrawings, as follows, Among the embodiments described below, the samenumber for the same part, or a part in an equivalent range, is utilized.

First Embodiment

FIG. 1 is a sectional drawing to roughly illustrate a main part of themounting structure utilizing the conductor composition of the firstembodiment according to the present invention.

The surface mounting component (20) is mounted on the mounting substrate(10), and the electrode (11) of the mounting substrate (10) and theelectrode (21) of the surface mounting component (20) are electricallyconnected through the electroconductive adhesive (30) which is theconductor composition. Hereinafter, the electrode (11) of the mountingsubstrate (10) is referred to as a substrate electrode (11), and theelectrode (21) of the surface mounting component (20) is referred to asa component electrode (21).

A printed substrate, a ceramic substrate, a lead-frame or etc. can beemployed as the mounting substrate (10), but there is no particularlimitation. The substrate electrode (11) is formed on one side of themounting substrate (10), and is constructed from a thick-film or metalplating utilizing a material of e.g. Ag-based metals such as Ag(silver), AgSn (an alloy of silver and tin), AgPd (an alloy of silverand palladium) etc., Cu-based metals such as Cu (copper), CuNi (an alloyof copper and nickel) etc., Ni-based metals or Au (gold) etc.

As the surface mounting component (20), an electronic component such asa capacitor, a resistance element, a semiconductor element etc. can beemployed. In the example shown in the drawing, the surface mountingcomponent (20) is shown as an example utilizing a chip capacitor. Thecomponent electrode (21) is also made from a metal. As the metal for thecomponent electrode (21), Au-based metals, Ag-based metals, Ni-basedmetals, Sn-based metals and etc. are utilized. As one example herein,the Sn-based metal is utilized.

FIG. 2 is a schematic drawing to illustrate the electroconductiveadhesive (the conductor composition) in a situation before curing. Theelectroconductive adhesive (30) is the conductor composition comprisingthe conductive particles (30 a) in conjunction with electricalconductivity, the solvent and also the binder resin (32). In FIG. 2, itis omitted to draw the solvent.

The conductive particles (30 a) are composed of the low crystallized Agfillers (31) with the crystal size of 10 nm or less.

In examples shown in FIG. 1 and FIG. 2, as preferable embodimentsaccording to the present invention, the conductive particles (30 a)comprise the low crystallized Ag fillers (31) and fine Ag particles (33)with a particle size of the order of nanometer adhering on surfaces ofcore particles which are the low crystallized Ag fillers (31).

In FIG. 1, a situation is shown where the substrate electrode (11) andthe component electrode (21) are connected through the electroconductiveadhesive (30), by using an electroconductive adhesive (30). This is asituation where, at the electroconductive adhesive (30) shown in FIG. 2,the solvent has evaporated, and the binder resin (32) is cured.

In a situation where the substrate electrode (11) and the componentelectrode (21), as shown in FIG. 1, are connected through theelectroconductive adhesive (30), the fine Ag particles (33) are mutuallyconnected electrically under the condition of being fused or sintered bymelting or sintering together. The substrate electrode (11), thecomponent electrode (21) and the fine Ag particles (33) are alsoelectrically connected under the condition of being fused or sintered bythe fine Ag particles (33) melting or sintering together.

Herein, it is due to a result of X-ray diffraction measurement that thecrystal size of each of the low crystallized Ag fillers (31) is 10 nm orless. The crystal size of the conventional Ag fillers utilized for thiskind of conductor composition has been generally several tens ofnanometers or more. The low crystallized Ag fillers (31) in thisembodiment have the smaller crystal size than the conventional Agfillers, in other words, are crystallized lower than the conventional Agfillers.

Specifically speaking, for example, the low crystallized Ag fillers (31)can be in the form of a sphere or a flake, and can have a particle sizewith a particle diameter of 0.1 μm or more and 20 μm or less.

In this example, for the fine Ag particles (33) adhered on the lowcrystallized Ag fillers (31), for instance, the particles with aparticle size in the range of 1 nm or more and 50 nm or less can beemployed. The amount of the adhered fine Ag particles (33) can be in therange of more than 0 wt % and about 50 wt % or less.

For the solvent, a solvent applied to a conventional electroconductiveadhesive can be utilized. For example, a solvent such as terpineol, etc.can be employed as the solvent.

In this electroconductive adhesive (30), the resin (32) is a mixturecomprising a main component, a curing agent, a reducing agent, adispersing agent for nano particles and a trapping agent for nanoparticles.

The reducing agent is added according to necessity, and may be notadded. The dispersing agent for nano particles and the trapping agentfor nano particles are necessary, in a case where the fine Ag particles(33) in this example are utilized. When these fine Ag particles (33) arenot utilized, the dispersing agents may not be added.

As the main component, a material selected from epoxy-based resins andmixed materials containing the epoxy-based resins can be employed, andthe material selected from phenol compounds and mixed materials thereofcan be employed.

The reducing agent is a compound which reduces a metal oxide layerformed on a surface of the component electrode (21) at a temperatureequal to or less than the curing temperature (generally from about 100°C. to about 200° C.) of the electroconductive adhesive (30). An agentselected from e.g. alcohol-based compounds, organic acid-basedcompounds, imidazole-based compounds etc. can be employed.

More concretely, as the reducing agent, trimethylolpropane,trimethylolethane, glycerol, tetraethylene glycol, diethylene glycol,ribitol etc. can be employed.

As mentioned above, in this example, as the preferable electroconductiveadhesive (30), particles are utilized which are formed by adhering fineAg particles (33) having a particle size of nanometer the order ofnanometer on surfaces of the low crystallized Ag fillers (31) which arethe core particles, by utilizing the low crystallized Ag fillers (31)with a crystal size of 10 nm or less as the core particle.

Such an electroconductive adhesive (30) can be prepared as follows. Byheating a mixture of the low crystallized Ag fillers (31) and the fineAg particles (33) in a solution or in a gas, a fusion or adhesion etc.due to sintering the fine Ag particles (33) onto the surface of the lowcrystallized Ag fillers (31) is carried out. The low crystallized Agfillers (31), of which the fine Ag particles (33) are located on thesurface, is formed by this process.

The temperature for this heating in a solution or in a gas is lower thanat least the curing temperature of the electroconductive adhesive (30),and an amount of sintered fine Ag particles (33) is kept low, so that areaction of the fusion or sintering of the fine Ag particles (33) canproceed in a curing process of the electroconductive adhesive (30) to becarried out later.

Then, the low crystallized Ag fillers (31), of which the fine Agparticles (33) are located on the surface, are mixed with the maincomponent and the curing agent and, if necessary, the reducing agent,further the dispersing agent for nano particles and the trapping agentfor nano particles, which construct the binder resin (32), as well asthe solvent together. Thus, the electroconductive adhesive (30) of thisexample is completed.

A method for connecting the surface mounting component (20) with themounting substrate (10) by utilizing the electroconductive adhesive (30)of this example formed in the manner mentioned above is described asfollows. FIG. 3 is a process chart to illustrate the method forassembling the mounting structure shown in FIG. 1.

At first, in a step for providing the electroconductive adhesive, theabove-described electroconductive adhesive (30) is provided on thesubstrate electrode (11) of the mounting substrate (10) by mask-printingor dispensing. After that, in a step for assembling the components, thesurface mounting component (20) is mounted on the mounting substrate(10) under the condition of being registered between the substrateelectrode (11) and the component electrode (21).

The steps until this process are carried out in atmosphere at the roomtemperature, and the electroconductive adhesive (30) is still un-cured.At this example, in the electroconductive adhesive (30) at thissituation, sintering of the fine Ag particles (33) is prevented due tothe situation where, as shown in FIG. 2, the dispersing agent for thenano particles coats the fine Ag particles (33), which are in the orderof nanometer, in other words the nano-particles. For the purpose, thelow crystallized Ag fillers (31) in the binder resin (32) are evenlydispersed in the resin (32).

After that, in a step for curing an electroconductive adhesive, theelectroconductive adhesive (30) is heated at the curing temperature fromabout 100° C. to about 200° C., and cured. By the step, the connectionbetween the surface mounting component (20) and the mounting substrate(10) is finished, and the mounting structure shown FIG. 1 is completelyformed.

In this curing step, a function as described below proceeds. Owing tothe heat during the curing step, an oxide layer formed on a surface ofthe component electrode (21) at the early stage is removed by a reducingagent, when a reducing agent is contained in the binder resin (32).

At this curing step, in this example where the fine Ag particles (33) ofnano particles are utilized, the trapping agent for nano particles trapsthe dispersing agent for nano particles wherein the fine Ag particles(33) are coated by the dispersing agent for nano particles and thetrapping agent for nano particles.

By the heat during the curing step, the fine Ag particles (33) adheringto the low crystallized Ag fillers (31) melt or sinter, and further bothsurfaces of the component electrode (21) and the substrate electrode(11) and the fine Ag particles (33) fuse or sinter together, and at thesame time the fine Ag particles (33) fuse or sinter to each other bymutually melting or sintering.

In other words, as described in FIG. 1, an electrically conductingformation by fusing or sintering of the fine Ag particles (33) is formedamong three parts of the component electrode (21), the low crystallizedAg fillers (31) (conductive particles (30 a)) and the substrateelectrode (11).

In this embodiment, the conductive particles (30 a) may be composed ofonly the low crystallized Ag fillers (31) with the crystal size of 10 nmor less, and free of the fine Ag particles (33) with a particle size ofthe order of nanometer.

In such a case, at the above-mentioned step for curing theelectroconductive adhesive, the low crystallized Ag fillers (31) causesfusion or sintering at the curing temperature of the binder resin (32),e.g. from about 100° C. to about 200° C. owing to that, intersticesamong particles of the low crystallized Ag fillers (31) and intersticesbetween the low crystallized Ag fillers (31) and each electrodes (11)and (21) are electrically connected under the condition of being fusedor sintered.

With respect to this matter, an experimental investigation was achieved.While a particular mechanism is not found, it seems to be based on abehavior that a low crystallized part has a tendency to stabilize bycrystallizing via heat treatment during the curing process, by utilizingthe electroconductive adhesive (30) composed of the low crystallized Agfillers (31) with the crystal size of 10 nm or less.

Due to the behavior, Ag can obtain the high conductivity by fusing orsintering, in the treatment at low temperature (e.g. about 150° C.) atthe same level as a conductor composition composed of only theabove-mentioned conventional fillers with a particle size of the orderof nanometer, even if the particle size of the conductive particles (30a), in other words the particle size of the low crystallized Ag fillers(31), is in the order of micron.

In other words, according to this embodiment, by utilizing the lowcrystallized Ag fillers (31) with the crystal size of 1 nm or less asthe conductive particles (30 a), for the electroconductive adhesive (30)as the conductor composition comprising the conductive particles (30 a)with electrical conductivity and the solvent, the electroconductiveadhesive (30) as the conductor composition, which can easily ensure theconductivity in the same level as the bulk Ag by the low temperatureprocess, can be provided.

In preferable embodiment examples of the present invention illustratedin FIG. 1 and FIG. 2, the electroconductive adhesive (30) is provided asthe conductor composition, wherein the conductive particles (30 a) arecomposed of the low crystallized Ag fillers (31) as core particles andthe fine Ag particles (33) with a particle size of the order ofnanometer adhering on the core particle's surface.

As described above, due to achieving the size of the order of nanometerby locating the fine Ag particles (33) with a particle size of the orderof nanometer around the low crystallized Ag fillers (31), an effect ofthe fine Ag particles (33) melting at low temperature can be achieved.

This seems to be based on a behavior that the fine Ag particles (33)with a particle size of the order of nanometer have a tendency tostabilize by decreasing their surface area. Due to the behavior, anachievement of high conductivity by the low temperature process isfurther promoted, and it becomes possible to fuse the electroconductiveadhesive (30) by a lower temperature process. Therefore, this embodimentis preferable.

For example, in the conventional conductor composition, a contactresistance between Ag fillers contacting each other by a pressure wasdominant, and its conductivity was 10⁻⁴ Ω·cm or more as volumeresistivity of the conductor composition.

In contrast, for the electroconductive adhesive (conductor composition)(30) described in FIG. 1 according to the embodiment of the presentinvention, its volume resistivity is from about 5×10⁻⁶ Ω·cm to about5×10⁻⁵ Ω·cm, and the conductivity is greatly improved.

In the embodiment of the present invention, a mounting structure isprovided, which utilizes a conductor composition comprising a mountingsubstrate (10) having an electrode (11) on one side of the substrate(10), and a surface mounting component (20) mounted on the electrode(11) of the mounting substrate (10), wherein the electrode (11) and asurface mounting component (20) are bonded through a electroconductiveadhesive (30), wherein conductive particles (30 a) in theelectroconductive adhesive (30) are composed of low crystallized Agfillers (31) of which the crystal size is 10 nm or less.

Accordingly, a mounting structure utilizing the conductor composition,which can easily secure the resistance in the same level as Ag bulk bythe low temperature process, can be provided.

In a preferable formation of this embodiment, the mounting structureutilizing a preferable conductor composition which can be handled atlower temperature is provided, by employing the mounting structurewherein the conductive particles (30 a) are utilized as core particles,and the fine Ag particles (33) with a particle size of the order ofnanometer are adhered on the core particles' surfaces.

In this embodiment, as one example, a Sn-based metal, wherein it hasbeen difficult in the past to make the resistance at a connecting partlow, is utilized as the component electrode (21) of the surface mountingcomponent (20). If the electroconductive adhesive (30) in thisembodiment is utilized, it can be easily achieved to make the resistancelow at the connection for the component electrode (21) utilizing thisSn-based metal.

Second Embodiment

FIG. 4 is a sectional drawing to roughly illustrate a mounting structureutilizing the conductor composition according to the second embodimentof the present invention. A different point from the above-mentionedembodiment is primarily described below.

The surface mounting components (20) are mounted on the mountingsubstrate (10), the substrate electrodes (11) of the mounting substrate(10) and the component electrodes (21) of the surface mountingcomponents (20) are electrically connected each other through theelectroconductive adhesive (30) as the conductor composition. Herein,the electroconductive adhesive (30) is the same as in theabove-mentioned embodiment.

In this embodiment, the mounting substrate (10) is formed by laminatinga plurality of resin layers 10 a, 10 b, 10 c and 10 d, made of theresin, and sintered.

In this mounting substrate (10), various kinds of wiring parts (12)-(14)are formed, and these wiring parts (12)-(14) are constructed from viaconductors (12), inner-layer wirings (13) formed inside the mountingsubstrate (10) and surface wirings (14) located at one side (upper sidein FIG. 4) of the mounting substrate (10).

The via conductors (12) are located at via holes formed in the variousresin layers (10 a)-(10 d), and the inner-layer wirings (13) are formedbetween the various resin layers (10 a)-(10 d). These wiring parts(12)-(14) are electrically connected each other. The surface wirings(14) are electrically connected with the substrate electrodes (11).

Herein, in this embodiment, the via conductors (12), the inner-layerwirings (13) and the surface wirings (14) are constructed from theconductor composition comprising conductive particles (30 a) withelectrical conductivity. This conductor composition is composed of thelow crystallized Ag fillers, wherein the conductive particles have acrystal size of 10 nm or less.

Specifically speaking, in the electroconductive adhesive (30)illustrated in FIG. 2, the conductor composition containing littlebinder resin (32), and containing the low crystallized Ag fillers (31)and the solvent is utilized. When high adhesive properties with thesubstrate etc. are necessary, for example, it may be an adhesive whereinan epoxy-based resin etc. of several wt % is added.

The via conductors (12), the inner-layer wirings (13) and the surfacewirings (14), described above, are formed, by patterning via a printingmethod, and heat-treating etc., with this conductor composition. Inthese wiring parts (12)-(14), an electrically conductive situation isensured, by vaporizing the solvent of the conductor composition, andfusing or sintering the low crystallized Ag fillers (31) each other.

In the conductor composition of this embodiment also, the composition ispreferred, wherein the conductive particles (30 a) are utilized as coreparticles, and the fine Ag particles (33) with a particle size of theorder of nanometer are adhered on the core particles' surfaces (see FIG.2).

When the above-described via conductors (12), inner-layer wirings (13)and surface wirings (14) are formed by using this conductor compositionwith a preferable formation, as illustrated in FIG. 1, the conductorcomposition is electrically connected under the condition of the solventbeing evaporated, and the fine Ag particles (33) fused or sintered bymelting or sintering the fine Ag particles together.

In this embodiment also, for example, each of the low crystallized Agfillers (31) can be in the form of a sphere or a flake, and the lowcrystallized Ag fillers (31) can have the size of the particle diameterof 0.1 μm or more and 20 μm or less.

Further, in this embodiment also, for example, particles with theparticle diameter in the range of 1 nm or more and 50 nm or less can beemployed as the fine Ag particles (33) adhering on the low crystallizedAg fillers (31). Then, the adhering amount of the fine Ag particles (33)can be in the range of beyond 0 wt % and about 50 wt % or less of thelow crystallized Ag fillers (31).

As the solvent, a solvent which can be applied for a usualelectroconductive adhesive can be utilized. For example, a solvent suchas terpineol, etc., can be employed as the solvent.

In the mounting structure shown in FIG. 4, the same one as described inembodiment above can be utilized as the surface mounting component (20),but it is not limited in particular. For example, as the surfacemounting components (20), a molded capacitor, a molded diode, a ceramiccapacitor etc. can be employed. In this example, a molded capacitor isshown as the surface mounting components (20).

Next, a method for forming the mounting structure illustrated in FIG. 4above is described. FIG. 5 including (a), (b), (c), (d) and (e) is aprocess chart showing a method for preparing the mounting substrate (10)in this forming method.

As a first step, as described in FIG. 5(a)-(c), holes (100) are formedat each of resin sheets (10 a)-(10 d) as plural resin layers, and theconductor composition of this embodiment comprising the conductiveparticles (30 a) and the solvent is filled in the holes (100) byscreen-printing etc., and the via conductors (12) are formed.

After that, the conductor composition is printed also on a surface ofeach of the resin sheets (10 a)-(10 d) in a desired pattern by thescreen-printing method etc. Thus, as shown in FIG. 5(d), wiring parts(12)-(14) composed of the via conductors (12), the inner-layer wirings(13) and the surface wirings (14) are formed.

As shown in FIG. 5(e), a laminated structure (110) is formed by stackinga group of resin sheets prepared in this manner, pressing and combiningthem in one unit. Further, by sintering the laminated structure (110),main substrate parts of the mounting substrate (10) are completed, andeach of the wiring parts (12)-(14) is sintered.

After sintering, the substrate electrodes (11) are formed by carryingout metal plating or thick-film printing at the surface wirings (14).Thus, the mounting substrate (10) is completed.

In this mounting substrate (10) utilizing the conductor compositionforming the surface wirings (14), the inner-layer wirings (13) and thevia conductors (12), the conductor composition contains conductiveparticles (30 a) with electrical conductivity, and the conductiveparticles (30 a) are composed of the low crystallized Ag fillers (31)with a crystal size of 10 nm or less.

After that, the electronic components are mounted on one side of themounting substrate (10). This mounting process is the same as the methoddescribed in FIG. 3 above.

In other words, in the step for providing the electroconductiveadhesive, the electroconductive adhesive (30) is provided on thesubstrate electrodes (11) of the mounting substrate (10) bymask-printing or dispensing. Then, in the step for assemblingcomponents, the surface mounting components (20) are mounted on themounting substrate (10) under the condition of being registered betweenthe substrate electrodes (11) and the component electrodes (21).

In a next step for curing the electroconductive adhesive, theelectroconductive adhesive (30) is heated at the curing temperature ofabout 100° C.-240° C., and cured. By this process, a connection betweenthe surface mounting components (20) and the mounting substrate (10) iscompleted, and the mounting structure described in FIG. 4 is formed.

By the way, in this embodiment, as in the above-described embodiment,the conductor composition comprising the conductive particles (30 a) inconjunction with electrical conductivity and the solvent, wherein theconductive particles (30 a) are composed of the low crystallized Agfillers (31) with the crystal size of 10 nm or less, and theelectroconductive adhesive (30) as such a conductor composition, areprovided.

In this embodiment, as in like the above-described embodiment, themounting substrate (10) utilizing the conductor composition is provided,wherein the mounting substrate comprises the mounting substrate (10)having the electrodes (11) on one side and the surface mountingcomponents (20) mounted on the electrodes (11) of the mounting substrate(10), and utilizes the conductor composition connecting the substrateelectrodes (11) and the surface mounting components (20) by filling thegap between them, and the conductor composition contains the conductiveparticles (30 a) with electrical conductivity, and the conductiveparticles (30 a) are composed of the low crystallized Ag fillers (31)with the crystal size of 10 nm or less.

Further, in this embodiment, the mounting substrate (10) utilizing theconductor composition is provided, wherein the surface wirings (14), theinner-layer wirings (13) and the via conductors (12) are formed with theconductor composition, the conductor composition contains the conductiveparticles (30 a) with electrical conductivity, and the conductiveparticles (30 a) are composed of the low crystallized Ag fillers (31)with the crystal size of 10 nm or less.

According to this embodiment, as in the above-described embodiment, byutilizing the conductive particles (30 a) composed of the lowcrystallized Ag fillers (31) with the crystal size of 10 nm or less, Agcan provide the high conductivity by fusing or sintering, in thetreatment at low temperature of the same level as a conductorcomposition composed of only the above-mentioned conventional fillerswith a particle size of the order of nanometer, even if the particlesize of the conductive particles (30 a) is in the order of micron.

In other words, according to this embodiment, the conductor compositionwhich can easily ensure the resistance at the same level as an Ag bulkby the low temperature process, the mounting structure utilizing theconductor composition, and the mounting substrate utilizing theconductor composition can be provided.

In this embodiment also, in a preferable formation or, in other words,in a case where the low crystallized Ag fillers (31) are utilized ascore particles, and the fine Ag particles (33) with a particle size ofthe order of nanometer adhere on surfaces of the core particles to formthe conductive particles (30 a), the effect can be achieved that the Agparticles (33) can melt at low temperature due to being made in theorder of nanometer.

Incidentally, while a laminated resin substrate was illustrated as anexample of the mounting substrate (10) in this embodiment, a laminatedceramic substrate may be utilized. A construction and a manufacturingmethod of the substrate are in conformance with the construction and themanufacturing method for the above-mentioned laminated resin substrate.

Other Embodiment

While the example, where chip-capacitors or mold-capacitors wereutilized as the surface mounting components, was described in theabove-mentioned embodiment, a component, etc., such as a capacitor, aresistor, a semiconductor element, an IC package etc. can be employed asthe surface mounting component. For example, a molded diode componentcomprising a lead made of copper as an electrode may be utilized as thesurface mounting component.

Further, in the above-mentioned embodiment, while the surface mountingcomponents (20) are mounted on the mounting substrate (10), and theelectrodes (11) of the mounting substrate (10) and the electrodes (12)of the surface mounting components (20) are connected via theelectroconductive adhesive (30), a step for packaging may be carried outafter carrying out such a mounting.

For example, while not being illustrated as a drawing, in the mountingstructure described in FIG. 1, a radiating plate composed of Al may befurther adhered on the substrate (a component mounting substrate), andthis radiating plate and a case may be further adhered and, after that,the structure may be sealed by silicone gel.

However, a formation of the package is not limited to theabove-described one, and the silicone gel may be used, or not used, andmay be substituted with other moisture-resistant coating material.

For example, in FIG. 1 described above, a connecting part of the surfacemounting component (20) with the mounting substrate (10) and itsperipheral parts may be reinforced by an under-fill resin. A sealingstructure using a mold resin also may be employed.

1. A conductor composition comprising conductive particles (30 a) with electrical conductivity and a solvent, wherein said conductive particles (30 a) comprises low crystallized Ag fillers (31) of which the crystal size is 10 nm or less.
 2. A conductor composition according to claim 1, wherein said conductive particles (30 a) comprise said crystallized Ag fillers (31) and fine Ag particles (33) with a particle size of the order of nanometer adhering on surfaces of core particles which are said low crystallized Ag fillers (31).
 3. A conductor composition according to claim 1, wherein each of said low crystallized Ag fillers (31) has a size of the particle diameter of 0.1 μm or more and 20 μm or less.
 4. A conductor composition according to claim 1, wherein each of said low crystallized Ag fillers (31) is in the form of a sphere or a flake.
 5. A conductor composition according to claim 2, wherein each of said fine Ag particles (33) has a particle diameter in the range of 1 nm or more and 50 nm or less.
 6. A conductor composition according to claim 2, wherein the amount of said adhered fine Ag particles (33) is 50 wt % or less of said low crystallized Ag fillers (31).
 7. A conductor composition according to claim 1, wherein the conductor composition comprises a binder resin (32) in conjunction with said conductive particles (30 a) and said solvent, and is applied as an electroconductive adhesive.
 8. A mounting structure utilizing a conductor composition comprising a mounting substrate (10) having one or more electrodes (11) on one side of the substrate (10), and one or more surface mounting components (20) mounted on said electrode(s) (11) of said mounting substrate (10), wherein said electrode(s) (11) and one or more surface mounting components (20) are bonded through a conductor composition (30), wherein said conductor composition comprises conductive particles (30 a), and said conductive particles (30 a) are composed of low crystallized Ag fillers (31) of which the crystal size is 10 nm or less.
 9. A mounting structure utilizing a conductor composition according to claim 8, wherein said conductive particles (30 a) comprise said crystallized Ag fillers (31) and fine Ag particles (33) with a particle size of the order of nanometer adhering on surfaces of core particles which are said low crystallized Ag fillers (31).
 10. A mounting structure utilizing a conductor composition according to claim 8, wherein each of said low crystallized Ag fillers (31) has a size of the particle diameter of 0.1 m or more and 20 μm or less.
 11. A mounting structure utilizing a conductor composition according to claim 8, wherein each of said low crystallized Ag fillers (31) is in the form of a sphere or a flake.
 12. A mounting structure utilizing a conductor composition according to claim 9, wherein each of said fine Ag particles (33) has a particle diameter in the range of 1 nm or more and 50 nm or less.
 13. A mounting structure utilizing a conductor composition according to claim 9, wherein the amount of said adhered fine Ag particles (33) is 50 wt % or less of said low crystallized Ag fillers (31).
 14. A mounting structure utilizing a conductor composition according to claim 8, wherein the conductor composition comprises a binder resin (32) and a solvent in conjunction with said conductive particles (30 a), and is applied as an electroconductive adhesive.
 15. A mounting substrate utilizing a conductor composition wherein one or more surface wirings (14) and one or more inner-layer wirings (13) and one or more via conductors (12) are formed with the conductor composition, wherein said conductor composition comprises conductive particles (30 a) with electrical conductivity, and said conductive particles (30 a) are composed of low crystallized Ag fillers (31) of which the crystal size is 10 nm or less.
 16. A mounting substrate utilizing a conductor composition according to claim 15, wherein said conductive particles (30 a) comprise said crystallized Ag fillers (31) and fine Ag particles (33) with a particle size of the order of nanometer adhering on surfaces of core particles which are said low crystallized Ag fillers (31).
 17. A mounting substrate utilizing a conductor composition according to claim 15, wherein each of said low crystallized Ag fillers (31) has a size of the particle diameter of 0.1 μm or more and 20 μm or less.
 18. A mounting substrate utilizing a conductor composition according to claim 15, wherein each of said low crystallized Ag fillers (31) is in the form of a sphere or a flake.
 19. A mounting substrate utilizing a conductor composition according to claim 16, wherein each of said fine Ag particles (33) has a particle diameter in the range of 1 nm or more and 50 nm or less.
 20. A mounting substrate utilizing a conductor composition according to claim 16, wherein the amount of said adhered fine Ag particles (33) is 50 wt % or less of said low crystallized Ag fillers (31).
 21. A mounting substrate utilizing a conductor composition according to claim 15, wherein the conductor composition comprises a binder resin (32) and a solvent in conjunction with said conductive particles (30 a), and is applied as an electroconductive adhesive. 